Stateside International Calling for Family Plans

Stateside International Calling for Family Plans

Basically, my question is: Are T-Mobile's stateside plans (the $10 and the $15 options) only charged once and available for all phones in a family plan? Or does it have to be added to each line separately? I ask because I was trying to do a trial run last night. I added my devices, my plan, and for the first line I picked the $15 stateside calling add-on. Then when it came to get add-ons for the second line, it wouldn't let me add that particular add-on (it said "added to cart" with a green check-mark). This is what makes me think that you buy it once and it's available for all phones in your family plan. Is this true? If it is, this is freaking amazing.

I looked at the total, and it only charged me the Stateside plan once.

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